An electric vehicle obtains its driving energy from electric energy, not by combustion of fossil fuels like existing vehicles. Such an electric vehicle has advantages of substantially no exhaust gas and very small noise, but the electric vehicle has not been put into practical use due to drawbacks such as heavy battery and long charging time. However, as serious pollution and exhaustion of fossil fuels become important issues, the development of electric vehicles is accelerated again. In particular, for putting electric vehicles into practical use, it is needed to make a battery pack serving as a power source into a lightweight and small design and also shorten its charging time, so the studies on such a battery pack are very actively made.
The battery includes a plurality of cells connected in series, and the cells generate heat when the battery pack is charged or discharged. If the heat generated from the cells are left as it is, the life of the cells is shortened. Thus, the battery pack is generally provided with a cooling channel for removing the heat generated from the cells.
The battery pack may be classified into Z-type battery packs and U-type battery packs depending on the shape of the cooling channel. In the Z-type battery pack, an air serving as a coolant is introduced into and discharged from the cooling channel in the same direction. Meanwhile, in the U-type battery pack, an air serving as a coolant is introduced into and discharged from the cooling channel in opposite directions. Hereinafter, a general U-type battery pack is explained with reference to FIGS. 1 and 2. FIG. 1 is a perspective view showing a general U-type battery pack, and FIG. 2 is a sectional view taken along the line A-A′ of FIG. 1.
The U-type battery pack 10 includes a plurality of cells 20 arranged to be connected in series, and cooling channels 30, 40 coupled to the cells 20. The cooling channels 30, 40 include a first cooling channel 30 coupled to an upper end of the cell 20 and a second cooling channel 40 coupled to a lower end of the cell 20.
One side 32 of the first cooling channel 30 is opened such that a coolant may be introduced therethrough. Also, in a portion of the lower surface of the first cooling channel 30, not coupled with the cells 20, a plurality of slits 34 are formed such that the introduced coolant may be discharged toward the cells 20.
In a portion of the upper surface of the second cooling channel 40, not coupled with the cells 20, a plurality of slits 44 are formed such that the coolant discharged from the first cooling channel 30 may be introduced. Also, one side 42 of the second cooling channel 40 is opened such that the coolant introduced through the slits 44 may be discharged out.
The coolant introduced through the side 32 subsequently passes through the slits 34, spaces between the cells 20, and the slits 44, and is then discharged out through the side 42. In this procedure, the coolant absorbs heat from the cells 20, thereby cooling the cells 20.
However, in the general U-type battery pack 10 configured as above, temperature deviation of the cells 20 is great, so lives of the cells 20 are seriously different from each other. Also, if some of the cells included in the battery pack run out, the entire battery pack should be exchanged, so living cells cannot be used any more due to the run-out cells. Thus, for solving the above problem, it is needed to study how to decrease temperature deviation of the cells 20.